Diabetes Mellitus (diabetes) is a leading cause of morbidity and mortality in the adult population. This is primarily because diabetic patients tend to develop vascular complications that involve the kidneys (diabetic nephropathy), the retina (diabetic retinopathy), as well as large and small blood vessels in other organs (macro- and micro-vascular disease) including nerves (diabetic neuropathy). It is well established that the vascular complications of diabetes are caused by elevated blood glucose levels over long periods of time. Elevated blood glucose levels affect proteins by a process known as glycation. Different “glycated” proteins have been identified in diabetic subjects, including albumin, hemoglobin and others. Measurement of the extent of protein “glycation” of certain proteins is considered a valuable clinical tool to assess long term glycemic control and thereby the efficacy of diabetes treatment.
Glycation, the non-enzymatic attachment of glucose to proteins, is considered a major pathophysiological mechanism causing tissue damage in diabetic subjects. Glycation involves the reaction of glucose and/or other reducing sugars with amino groups in proteins resulting in the formation of a Schiff base or aldimine. This labile adduct can tautomerize via the Amadori rearrangement to the more stable ketoamine. The function of the glycated protein may be impaired, depending on the location of the amino group(s) affected. For example, amino-terminal glycation of the β-chains of hemoglobin gives rise to the glycated hemoglobins (HbAl) in which responsiveness to 2,3-diphosphoglycerate is decreased and oxygen affinity increased. Glycation of the major thrombin inhibitor of the coagulation system, antithrombin III, decreases its affinity for heparin, and has been postulated to contribute to the hypercoagulable state associated with diabetes.
Mass spectrometry has been used for the examination of protein glycation in diabetes research. Low- and high-resolution mass spectra, GC/MS, collisional activation spectroscopy, ESI, and MALDI/MS have been used in research settings for structural identification and quantitative assessment of glycation end products and glycation of proteins. (Lapolla, A, et al., Mass Spectrometry Reviews, 2000, 19:279-304). These methods can be time-intensive and the markers for assessing glycation levels and related effects of increased glycation in diseases such as diabetes are not optimal or applicable for rapid, reliable clinical applications.
In the clinical assessment of diabetes, protein glycation in diabetic subjects is currently measured in blood by estimating the amount of glycated hemoglobin (hemoglobin A1c) through a complicated clinical test that requires extraction of a blood sample. Accordingly, there is a need for a simplified, faster, and less invasive method for rapid monitoring of protein glycation levels.